Treatment of concentrates



Feb. 26, 1923.

W. O. BORCHERDT TREATMENT OF CONCENTRATES Filed June 4, 1919 affozneqs Patented Feb. 2%, 19 23.

WALTER O. BORCHERDT, OF AUSTINVILLE, VIRGINIA,

ias

r E F ABSIGNOR TO THE NEW JERlSEY ZINC COMPANY, OF NEW YORK, N. Y., A CORPGRA'I'ION OF NEW JERSEY,

TREATMENT or concmaarns.

Application filed June 4, 1919. Serial No. 301,833.

1'0 all whom it may concem:

Be it known that I, WALTER 0. Bon- CHERD'I', a citizen of theUnited States, residing at Austinville, in the county of l/Vythe, State of Virginia, have invented certain new and useful Improvements in the Treatment of Concentrates; and I do herebydeclare the following to be a full, clear, and exact description of the invention, such as will enable others skilled in the art to which it ap-pertains to make and use the same.

This invention relates to the treatment of mineral concentrates, and more particularly to the treatment of flotation concentrates produced in the flotation of ores with the aid of oil or other flotation agent.

i The froth produced in the flotation process is frequently of a persistent character which does not break readily on standing. The persistence of the froth, when the ore pulp contains considerable amounts of colloidal slime, is due largely to the colloidal constituents which are carried into the froth. Frommy experience with froth produced from ore pulp carrying considerable amounts of colloidal slime, I have been led to believe that such colloidal constituents are comparable in importance to the oil or other flotation agent which is present during the flotation and Which to a greater or less extent combines with the mineral particles and with the air and water to form the froth. When the ore pulp is rich in colloidal slimes greater dilution thereof during flotation is commonly necessary and an over-stabilized froth is frequently produced and gives a dirty concentrate. The condition of the froth indicates that the colloids are to a greater or less extent adsorbed by the mineral particles or are otherwise combined therewith and with the water and other constituents of the froth so that they increase the stability and permanence' settling or sedimentation facilitated.

The colloidal constituents of ore pulps are rarely, if ever. naturally deflocculated and dispersed to their maximum possible extent. Since aggregated or flocculated colloid masses act like solid particles of greater magnitude the removal of the partially fiocculated colloidal constituents of an ore pulp by means of settling processes, or even washing with water on tables or vanne'rs, is generally incomplete and inadequate. The agencies which promote the flocculation of the colloidal constituents of an ore pulp also in general seem to promote the adsorption or other form of attachment which exists between such colloidal constituents and the granularconstituents of the ore pulp. It follows, therefore, that when the colloidal constituents of an ore pulp have been thoroughly deflocculated and minutely dispersed they no longer exist in the form of aggregates resembling the coarser solid particles of the pulp,"- but behave more like substances in solution, and are, in fact, spoken of as being in colloidal solution, in which condition the forces tending to maintain them in suspension are greater thanthe effect of gravity, thereby greatly facilitating their separation .by sedimentation and decautation, and as, at the same time their adsorption or other bond for the coarser solid particles of the ore pulp is weakened, the removal of such colloidal constituents from the ore pulp is greatly facilitated over what is possible in their natural. partially ment of the pulp, they may have become flocculated during the treatment to which the pulp is subjected or agents may have been added which cause them to flocculate, and in such cases the same general method of treatment is applied to secure deflocculation in accordance with the rinciples of this invention as would be app ied to a pulp containing naturally flocculated colloidal constituents. Thus, where a flocculating or coagulating agent has been added to the ore pulp to bring about coagulation or flocculation of'the colloidal slimes, and where coagulated o1 flocculated constituents are carried into the froth and .concentrate,-the concentrate or froth is subjected to a further treatment with an agent or agents which will serve to change the state of the colloidal particles from the flocculated to the deflocculated or dispersed state. The

agent .to be added posite character,

will generally be of an opin its action upon the colloidal constituents, from those which may have been used to effect the flocculation 1n so-called colloidal polarity (whether electropositive or electro-negative) of the particular ingredients of the concentrate being treated and upon other similar conditions. With some ores I have found sodium silicate well adapted for use in bringing about the desired dispersion; but the nature of the agent or agents to be employed in any particular case may be readily determined by means of the common tests applied in "colloid chemistry.

Various substances, organic or inorganic, such as salts, acids and alkalies, or even sub stances which are themselves colloidal in nature may be used as the deflocculating or dispersing agent.

The dispersing agent will usually be required only in small amount, for example, a few pounds or less per ton of concentrate. The dispersing agent may be intimately ea er? hot water where direct heating is not practicablezand cooling may be accomplished by passing the pulp over cooling towers with evaporating trays, or by dilution with cold water.

Simple tests, which may be made with small quantities of concentrate pulp, as for example, one liter samples, and which may number of pulp samples of the same volume.

mixed with the concentrate in any suitable manner and with dilution of the concentrate pulp to promote the inter-mixture.

The distribution of the deflocculating agent through the concentrate pulp and its intimate mixture therewith may be pipes or launders,

brought about by agitating the deflocculating agent with the pulp by any commonly understood means, as by adding the agent to the pulp previous to the passage of the latter through pumps, by mechanical agitation or by the use of steam, air or water jets.

If the concentrate pulp is to be diluted with water it is generally desirable to dissolve or disperse the defiocculating agent in the dilution water before adding the latter to the pulp and then toagitate the diluted pulp to the required degree. When the dis persion has been brought about the mineral particles of the froth o-r concentrate willbe freed to such an extent as will permit their separation by settling or sedimentation. The concentrate will thus be enriched by the elimination of the colloidal gangueconstituents and by the separation of practically all except the intersticial water, so that the con centrate can be recovered with a low water content comparable to that of a concentrate obtained by vacuum filtration or filter press:

Tt may also be desirable in special cases to heat or cool the concentrate pulp above or below its natural temperature to hasten or facilitate the defiocculation of the colloidal constituents.

Heating the pulp may be accomplished by commonly of steam jets or steam coils, or dilution with understood means such as the use concentrates,

thrown away, or, if

One of these. is decanted and evaporated to determine the dry Weight of solids in each sample, thus furnishing the basis for determining the relative quantity of deflocculatirijg agent used and thedegree of dilution. l hen a sample is to be tested it is brought to the desired density and temperature, a measured quantity of a certain deflocculating agent is added and the sample is shaken in a shakin machine for a definite period. It is then a lowed to stand quietly and the degree of permanence of the suspension of the deflocculated colloidal constituents and the rate of settling of "the mineral concentrates are observed for definite intervals and recorded for comparison with other tests. When the concentrate has completely settled the cylinder is jarred until the layer of concentrate reaches. its minimum volume. This is read ofi of the graduated scale and recorded. Y

By var-yin one by one the factors of dilutioil, defloccu ating agent, agitation, temperature, and time the best and most economical set of conditions for any given concentrate may be-readily found and the working practice made to conform. The optimum condition for the purposes of this invention is that in which a given weight of concentrate settles after treatment to the minimum Volume with the minimum moisture content, and'most complete exclusion of the water, flotation agent, colloidal constituents. and gangue particles.

The colloidal constituents from which the mineral is permitted to separate may be it contains values, it maybe separately treated for the recovery of the values therefrom, for example, by returning it to the flotation process and subjecting it to a further flotation operation.

The process of the present invention is applicable to other concentrates than. flotation loidal constituents in a flocculated or coaguwhich are contaminated by collated state. The process is of particular value, however, in the case of flotation concentrates for the reason that the concentrate also contains part of the flotation agent employed, which further serves to prevent the ready separation by settling or sedimentation of the mineral particles from the accompanying water and colloidal slime,- and the treatment applied to effect the deflocculation of the colloidal constituents also generally results in the separation of a large part of the flotation agents from the concentrate.

- This results from the fact that the treatment which efiect/s the defiocculation or dispersion of the colloids generally breaks any oil emulsions which may exist, and in general facilitates the separation of the agents used for flotation from the mineral particles of the concentrate.

The dispersion of the colloidal constituents of the concentrate is generally more effective when the pulp containing the concentrates is alkaline. Where the concentrate pulp is normally acid, it is, therefore, generally desirable to addsome agent to render it neutral or sli htlyalkaline before proceeding with the dispersion of the colloidal constituents. I have found sodium silicate, acacia (gum arabic) and foundry molasses particularly effective defloccula'ting agents, when-used in a neutral or alkaline pulp. v V

It is well known that many colloids have such marked power for adsorbing or otherwise combining with water that they are known as hydrophyllic or water-loving and it seems probable that much of the difficulty which is experienced in separating the water from finely divided mineral concentrates by settling, sedimentation, filtration,"

centrifuging and drying is due to the presence of such material, which holds to water withextreme tenacity.

Such swollen sub-microscopic masses may also be conceived of as existing in the intersticial spaces between the mineral particles and preventing these particles from packing together as closely as would otherwise be possible, thus causing the mass of concentrates to retain an undue amount of water.

lVhen the colloidal constituents of an ore pulp are present in a fiocculated or coagulated form the floccules tend to obey gravity like coarser particles and in a settling pulp the rate of fall of the coarser particles is reduced by the hindrance which they meet from these swollen flocculent agglomerations', which move out of the way but slowly; and in the later stages of settling give the coarser particles the appearance of settling in a highly viscous medium. In a settled mass of concentrate which has apparently reached equilibrium, that is, where the mass seems to be settled as far asit can go, the presence of the the fioccules seems to. partly prevent contact between mineral particles, so that a much greater amount of water is held betweenthemineral particles than would be possible if they were in the most intimate possible mechanical contact with one another.

When such an apparently settled mass is disturbed, by gentle stirring or otherwise, the equilibrium is often broken, so that water channels form,'with rapid ascending currents, which carryout some of the flocculent material and permit of the mineral matter settling into a more compact mass, holding much less water.

Regardless of whether or not there is any difi'erence between the amount of water which a fiocculated or a "dispersed colloid can hold to itself, there is a great advan tage in deflocculating or dispersing the colloidal constituents of a concentrate pulp, because when dispersed uniformly throughout the entire amount of water associated with the mineral in a concentrate pulp the colloid particles practically lose their tendency to settle with the coarser particles; the rate of settling of these coarser particles is no longer hindered by their presence, so that the appearance of increasing viscosity of the medium is absent, and, while the degree of concentration of the dispersoid is prob ably the same in the water of the intersticial spaces of the settled concentrate as in the body of the supernatant liquid; the degree of concentration of the colloid per unit of watercan be reduced to any desired point by the simple expedient of diluting the concentrate pulp with water as much as is necessary before settling it.

So marked is the effect of deflocculating the olloidal constituents of a mineral pulp, upon the settlement of the mineral particles, that in a mixed concentrate of several mineral species, where the particles have approximately the same diameter but differ in specific gravity, the mass, upon settling, separates into more or less distinct layers or bands, with the heaviest mineral species in the lowest band, and the lightest in the upper band. This action is supposed to be due to the classifying action of the intersticial water currents and is a special case of hindered settling, such as occurs in the old concentrating device known as the kieve used in Cornish. tin dressing practics, and it is facilitated by bumping or vibrating the kieve or tank in which the settling takes place; but by dispersing the colloids by the process of the present invention this action is intensified to such a degree that an additional separation of the 'minerals may in certain cases be made possible, and the vibration or bumpin of the settling tank or the movement of c ains or stirring arms in the tank can be taken advantage of to secure a still more perfect separation of the water and colloids from the mineral concentrate.

The process of the present invention can he carried out with good results in any settling tank of the types commonly used in the arts. regardless of Whether these are continuous tanks of the type known as Dorr, Allen. or Callow, which are continuously fed with dilute pulp and from which a substantially clear overflow and greatly thickened underflow or spigot discharge are taken; or of the discontinuous or intermittent type in which pulp is fed to a tank which is allowed to fill up with settled concentrate and the pulp is then switched to another tank while the first tank is relieved of the supernatant water and the concentrate is then drawn through holes in the bottom, shoveled out, or otherwise removed.

In the application of the process of the present invention it will be obvious that it is advantageous to settle the concentrate in relatively deep tanks if it is desired to secure the utmost possible removal of water without having recourse to mechanical means such as kieving, filtration or centr1- fuging; since my making deep layers of the heavy minerals forming the bulk of the concentrate the weight of the material is correspondingly more effective in squeezing the water out of itself. l

As an example of the commercial application of the process of the present invention in the. removal of water from a flotation concentrate I will cite the following case in which a tank 18 inches square and 12 feet high was fed with the flotation zinc concentrate from a Callow recleane-r cell for seven hours, the nearly clear overflow being led away.

The pulp fed to this tank contained about 50% mineral by weight and the tank had I suspended in it two chains 10 inchesapart which were hung from a spring board and were shaken at about 15 minute intervals.

After filling, the tank stood for about 30 hours before it was convenient to empty it,- and the supernatant water was then decan'ted off and the tank dug out. An average of three samples showed a moisture content of the concentrate of 12 per cent. This Zinc concentrate was all through 100 mesh material. Other operations in the same tank showed for flotation lead concentrates moisture contents as low as from 7% to 9%.

It should be noted that when the colloids in the concentrate are not sufliciently detlocculated by the treatment which they have received previous to and during flotation and it is necessary further to deflocculate them by the addition of an agent such as sodium silicate, gum arable, or foundry molasses,- that it is sometimes very advantageous to add this agent to the pulp entering the final flotation cleaning cell. The

effect is to give a more brittle and more highly mineral-selective froth on that cell,

so that less gangue and less colloid matter go over into the concentrate with the final froth and the concentrate then still contains sufficient deflocculating agent to serve the purposes of the present invention. By thus adding an appropriate deflocculating agent to the feed to the last cleaning cell of the flotation apparatus, where the final concenti te is produced, there is secured a cleaner concentrate, and at the same time there is secured in the final concentrate pulp the presence of the requisite amount of the deflocculating agent to effect the desired dispersion of the colloidal constituents in the pulp for effecting the separation of the mineral constituents from the dispersed colloids and the bulk of the water in accordance wi-ththe principles of the present Gangue particles present in the concentrate pulp, if lighter than the mineral particles, will settle more slowly than the latter, and, in general, will be continually carried in the upper layer as the mineral particles settle,

heavy mineral particles,

and such gangue particles may accordingly be largely removed with the supernatant water or effluent, thereby facilitating the separation of the gangue particles from the mineral concentrate. This removal of gangue particles from the final flotatiion concentrate, as well as the removal of the colloidal constituents, in accordance with the inve'ntion, raises the grade of the final concentrate.

As previously pointed out, the method of the invention also generally effects the removal of the greater part of the flotation, agent from the concentrate. The presence of flotation agents, such as oils, in the concentrate are often undesirable and objectionable from'the smelters standpoint, and this is particularly true in the case of blende which is to be roasted for sulphuric acid manufacture, since it is generally supposed that the carbonized oil has a tendency to darken the acid.

The dispersion of the colloidal constituents in the concentrate pulp and their removal therefrom by sedimentation of the granular particles and decantation of the colloid-hearing water, or otherwise, may be ea er? employed with advantage as a preliminary step in the dehydration of the concentrate. Thus, the method of the invention may be practiced as a preliminary step in the preparation of the concentrate for vacuum or pressure filtration, or in the preparation of the concentrate for drying, or in the preparation of the concentrate for centrifuging where the concentrate removed from the Water or the water is removed from the concentrate by centrifugal action.

In treating concentrate pulps'in accord ance with the present invention, it is desirable, as hereinbet'ore explained, to separate the mineral constituents from the dispersed colloids and the bulk of the water. thereby securing a final concentrate containing a relatively small proportion of moisture, and to this end the manner of removing the dispersed colloids, together with the bulk of the water will be chosen to suit the particular case in hand, having in mind the character of any subsequent treatment to which the final concentrate may be subjected tor effecting the desired dehydration thereof. Throughout this specification and the appended claims, I intend to embrace in the expressions colloids and colloidal constituents both true colloids and those quasi or borderland substances, which may not be truly colloidal but partake of the qualities of, or resemble. colloids, and without regard to the sources from which such colloidal matters are derived. Thus, for the purposes of the present invention, the colloidal constituents may be considered as ranging from just above the molecular size upward through the class of so-called suspensoids. which. while possibly not true colloids, still, because of their relatively large specific surface. exhibits some, if not all. of the properties of colloids, and are capable of existing in both the sol or gel state, or of being dispersed and coagulated, or fiocculated and deflocculated. and are amenable to the manipulation herein described.

An apparatus which 1' have found particularly suitable to the application of the process of the presentinvention is illustrated in the single figure of the accompanying drawing.

This apparatus comprises a platform 1 upon which is mounted a. tall settling tank 2. The interior vertical section of this tank has the configuration of a trusturn of a cone. At the bottom. the tank 2 is provided with a cleanout door 3 through which the settled concentrates may be removed. During sedimentation or settling. the door 3 is closed by a door-plate fidesigned to make a watertight joint therewith. During the cleaning out operation, the door 5 may be swung out of the Way by means ct pulleys 7 suspended from a six port 8 securedto the upper ends of the tan 2?.

A trough 9 is provided for the reception of the settled concentrates, from which the concentrates may be dug out by a car-loading elevator 10 mounted on tracks 11 in front of a system of tanks 2. The car-loading elevator l0 discharges the concentrates into a car 12 standing on tracks 13, the latter also running in front of the series of tanks 2.

The concentrate pulp is delivered to the tank 2 through a perforated pipe 16 having a valve 15 for controlling the pulp supply. The pipe 16 extends throughout the entire length of the tank 2 and is perforated throughout its whole length, whereby the concentrate pulp can be fed into the tank without disturbance of the contents thereof. An overflow pipe 17 serves to conduct the supernatant water to a settling tank (not shown). An overflow pipe 18, equipped with a valve 19. is.provided for removing the layer of middlings or gangue which covers the concentrate when the tank is full. and is arranged to discharge such middlings into a ditch 20.

Brackets 23, mounted on top of the tank 2. support bearings 24, in which ismounted a shaft 25 carrying an arm 26, from thecnds of which are supported stirring chains 27. The chains 27 are secured at the bottom of the tank by eye-bolts 28. The shaft 25 and the arm 26 are rocked by means of a crank arm 29' which receives its motion by means of a rod 30 pivoted to a gear wheel 32 by a pin 31. The gear wheel 32 may be driven by an appropriate motive means indicated at in the drawing. The rocking of the arm 26 draws the chains 27 taut in one position and allows them to fall slack in another position thereby promoting the dense packing of the concentrate hereinbefore referred to.

It will be evident to those skilled in the artthat the present invention, considered as a method for reducing the moisture content of mineral concentrates. involves deflocculating or dispersing the colloidal constituents of the concentrate pulp. diluted if necessary. and subjecting the pulp first to free settling. during which the mineral grains settle freely and rapidly. while the colloidal constituents remain in suspension. and the gangue particles. if present. which are generally smaller and lighter than the mineral particles. tend to settle more slowly than the latter. As a result of this first stage of action. the mineral particles settle in a layer at the bot-tom and the gangue particles arrange themselves above this settled mass. while the bulk of the water. which contains the dispersed colloidal constituents and any flotation or other agents which may have been present. is separated and stands above the sediment.

As further additionsof pulp are made. the action in the zone of free settling continnes, and the colloid bearing water gradually passes out of the, tank by displacement while the sediment increases in depth.

Within the mass of settled Concentrate or sediment further action is taking place during all this time. The concentrate mineral particles crowd one another setting up interstitial currents of the water which they displace. These interstitial currents, in forcing their way out ofvthe mass, create the conditions of hindered settling and carry with them the gangue and other" articles which are too light or too smal to maintain themselves in a lower ositio'n. The colloidal constituents being ispersed or in the sol condition are unable to attach themselves to theconcentrate mineral particles and behave as though they were in solution in-the water, passing out of the settling mass with the water.

hen the concentrate mineral particles first come into contact with one "anotherto form a definite layer of sediment, the volume of interstitial water displaced is so great that it forms pipes or channels, in order to escape. This phenomenon is quite evidently due to the fact that by forming such channels water can escape by movin laterally in part until the channels are reached, and then vertically through them and this is easier for it at that stage than for all of it to escape vertically. Later on,

as the amount of interstitial water is reduced by such escape, the volume is insufficient to keep these pipes or channels open and they collapse. on escape of the water occurs in a series of tiny, substantially vertical, interstitial streams, and it is at this stage that gently stirring or vibration, which facilitates the action of gravity by reducing the friction between particles, becomes effective in reducing the interstitial space and therefore the amount of water which'can be held by the settled mass of concentrate.

We have, therefore, free settling in the dilute pulp; hindered settlingin the upper portion of the sediment, and compacting (an extreme phase of hindered settling) in the lower portion of the sediment;

this last stage being facilitated by the gently stirring or vibration hereinbefore referred to, and being similar to the action which takes place in a kieve during pounding, and all of these actions are facilitated and the final extreme reduction in moisture content is rendered possible by the deflocculation of the colloidal constituents of the pulp, which prevents such constituents from mingling with, attaching themselves to and holding water between the granular particles.

The term hindered settling, as used in this specification and the appended claims, is intended to describe the condition which exists within the-,mass of 'particles which From this point.

have assumed a stratified condition, such that the particles are crowding one another and by their further settlement displace the interstitial water, which, rising between them, exercises a sorting action that tends to force the lighter and smaller particles upward, which action is preferably further assisted by gentle stirring or vibration to over come the mechanical friction of the particles upon one another, and the terminal stage of which is a close and compact deposit.

ll claim? p I 1. The method of treating a mineral concentrate containing colloidal constituents, which comprises subjecting the .concentrate to a deflocculation or dispersion treatment for defiocculating or dispersing the colloidal constituents and forming a concentrate pulp containing the colloidal constituents in a deflocculated or dispersed condition, and separating the mineral constituents from the dispersed colloids and the bulk of the water by hindered settling and thereby obtaining a mineral concentrate freed of the colloidal constituents which remain with the bulk of the water.

2. The method of dewatering a wet fiotation concentrate containing colloidal constituents which comprises subjecting the concentrate. to a deflocculation or dispersion treatment for deflocculating 01' dispersing the colloidal constituents and forming a concentrate pulp containing the colloidal constituents in' a defiocc'ulated or dispersed condition, and separating the mineral constituents from the dispersed colloids and the bulk of the water by hindered settling 1 and thereby obtaining a mineral concentrate freed of the colloidal constituents which remain with the bulk of the water and having a moisture content less than that of the dispersed colloids and the bulk of the water by sedimentation in the course of whichrelatively free settling of the mineral particles first takes place followed by hindered settling and finally by compacting of the mineral particles, and thereby obtaining a.

mineral concentrate freed of the colloidal constituents which remain, with the bulk of the water and having a moisture'content less than that of. the original mineral concentrate.

4:. The method of dewatering a wet flotation concentrate containing colloidalconmace-r7 stituents which comprises subjecting the concentrate to a deflocculation or dispersion treatment for deflocculating or dispersing the colloidal constituents and forming a concentrate pulp containing the colloidal constituents in a deflocculated' or dispersed condition, and separating the mineral constituents from the dispersed colloids and the bulk of the water by sedimentation in the course of which relatively free settling of the mineral particles first takes place followed by hindered settling and finally by compacting of the mineral particles and thereby obtaining a mineral concentrate freed of the colloidal matter which remains with the bulk of the water and having a moisture content less than that of the original flotation concentrate.

5. The method of enriching mineral concentrate pulps containing colloidal constituents and gangue particles which comprises subjecting the pulp to a deflocculation treatment for dispersing the colloidal constituents, and separating the mineral constituents of the pulp from the dispersed colloids and the gangue particles and the bulk of the water; by hindered settling.

6. The method of enriching a mineral concentrate pulp containing colloidal constituents and gangue particles which comprises subjecting the pulp to a deflocculation treatment for dispersing the colloidal constituents, and separating the mineral constituents of the pulp from the gangue particles and the bulk of the water containing the dispersed colloidal constituents by sedimentation and decantation in the course of which relatively free settling of the mineral con stituents in a relatively dilute pulp first takes place followed by hindered settling and finally by compacting of the mineral constituents.

7. The method of enriching mineral concentrate pulps containing gangue particles which comprises subjecting the pulp to hindered settling in the presence of a dispersed colloid, and removing the gangue particles and the bulk of the water together with the dispersed colloid from the mineral particles of the pulp by decantation.

8. The method of treating flotation concentrates containing a flotation agent which comprises subjecting the concentrate pulp to sedimentation in the presence of a dispersed colloid, and removing the flotation agent and the bulk of the water together with the dispersed colloid from the mineral particles of the pulp by decantation.

9. The method of treating flotation concentrates containing colloidal constituents, gangue particles and aflotation agent which comprises subjecting the concentrate pulp to a deflocculation treatment for dispersing the colloidal constituents, and separating the mineral particles from the bulk of the water and the dispersed colloids together with the flotation agent and the gangue particles. v v

10. The method of treating flotation concentrates containing a flotation agent which comprises subjecting the concentrate pulp to sedimentation in the presence of a dispersed colloid whereby the mineral particles of the pulp are permitted to settle leaving the flotation agent in suspension, and separating the mineral particles from the bulk of the water and the suspended flotation agent.

11. The method of treating a wet mineral concentrate containing colloidal constituents which comprises dispersing the colloidal constituents and diluting the concentrate pulp with water to reduce the degree of concentration of the dispersed colloids per unit of water, and removing the mineral particles of the concentrate pulp from the dispersed colloids and the bulk of the water by sedimentation in the course of which relatively free settling of the mineral particles in a relatively dilute pulp first takes place followed by hindered settling and finally by compacting whereby there is obtained a mineral concentrate freed of the colloidal constituents which remain with the bulk of the J Water and having a moisture content less than that of the original mineral concen trate.

12. The method of treating a Wet mineral i concentrate containing colloidal constituents which comprises subjecting the concentrate to a defiocculation or dispersing treatment for deflocculating or dispersing the colloidal constituents and forming a concentrate pulp containing the colloidal constituents in a dispersed or deflocculated condition, and separating the mineral particles from the dispersed colloids and the bulk of the water by sedimentation in the course of which relatively free settling of the mineral particles in a relatively dilute pulp first takes place followed by hindered settling in the np per stratum of the settling particles and compacting in the lower stratum of the settling particles whereby there is obtained a mineral concentrate freed of the colloidal constituents which remain with the bulk of the water and having a moisture content-- less than that of the original mineral concentrate.

13. The method of preparing a mineral concentrate pulp containing colloidal constituents for dehydration by filtration, centrifuging, drying, or the like, which comprises subjecting the pulp with the colloidal constituents present in a dispersed condition to sedimentation in the course of which relatively free settling of the mineral particles first takes place followed by hindered settling and finally by compacting of the mineral'particles and therebyiobtaining a mineral concentrate having a moisture content less than that of the original mineral concentrate pulp.

14. The method of preparing a mineral prises subjecting the pulp to a deflocculation treatment for dispersing the colloidal constituents, and separating the mineral constituents of the pulp from the dispersed colloids and the bulk of the water by sedir mentation in the course of which relatively free settling of the mineral particles first takes place followed by hindered settling in the upper stratum of the settling particles and compacting in the lower stratum of the settling particles and thereby obtaining a mineral concentrate having a moisture content less than that of the original mineral concentrate pulp.

15. The method of treating a normally acid mineral concentrate pulp containing colloidal constituents which comprises neutrali zing the acidity of the concentrate pulp, subjecting the pulp to a deflocculation treatment for dispersing the colloidal constituents, and separating the mineral constituents of the pulp from the dispersed colloids and the bulk of the water.

16. The method of enriching a flotation concentrate which comprisesadding a colloid dispersing agent tQ. the feed to a cell of the flotation apparatus, subjecting the resulting flotation concentrate to a defloccu-.

lation treatment for dispering the colloidal constituents contained in the concentrate,

and separating the mineral constituents of the pulp from the dispersed colloids and the bulk of the water.

17. The method of treating a mineral concentrate pulp which comprises subjecting the pulp in a condition of relative dilution thereon, and separating the settled mineral particles from the bulk 'of the water contain-- ing the dispersed colloidal matter.

18. The method of treating a wet mineral concentrate containing colloidal constituents, which comprises subjecting the concentrate to a deflocculation or dispersion treatment for deflocculatlng or dispersing the colloidal constituents and forming a concentrate pulp containing the colloidal constituents in a defiocculated or dispersed condition, and separating the mineral constituents from the dispersed colloids and the bulk of the water by hindered settling and thereby obtaining a mineral concentrate freed of the colloidal constituents which remain with the bulk of the water and having a moisture content less than that of the original mineral concentrate. y

In testimony whereof llaflix my signature.

.WALTER O. BORGHERDT. 

